1. Field of the Invention
The present invention relates to the cleaning of fabrics used in papermaking, and, more particularly, to cleaning fabrics with a low air permeability (i.e., semipermeable membranes).
2. Description of the Related Art
The need to clean fabrics of papermaking machines is well known. Since the flow of air and/or water through such fabrics is relied upon during the paper forming process, it is desirable that a maximum number of the fluid pathways available in such fabrics remain open. However, during transport of a paper web using such fabrics, various debris that is a by-product of the papermaking process can and does manage to get caught within the fluid pathways of such fabrics. This ongoing collection of debris in a fabric can reduce fluid flow rates therethrough to unacceptable levels and, if collecting near the surface of the fabric, can directly affect the surface quality of the paper being produced. Consequently, the need to effectively clean such fabrics exists.
A variety of methods and devices have already been developed for cleaning fabrics of papermaking machines. It has been disclosed to use different kinds of brushes, air jets and ultrasound spray bars. A rotatable needle jet has also been employed for cleaning fabrics. It has further been suggested to use water spray devices in combination with blowing air to clean a forming wire or screen.
However, these solutions have all been found suitable for cleaning forming wires, press belts and drying fabrics with a high air permeability. These solutions have not been found effective for cleaning low air permeability (i.e., semipermeable) fabrics. In fabrics with high air permeability, the fluid pathways tend to be both numerous and relatively large. As such, debris can be dislodged relatively easily from most such pathways, and there are enough fluid pathways available that it may not always be critical to achieve a high degree of cleanliness for the fabric to operate sufficiently.
However, in semipermeable fabrics, in order to obtain the desired low air permeability therethrough, the number of fluid pathways tend to be limited and/or relatively small, in comparison to high air permeability fabrics. Thus, removal of debris from pathways of semipermeable membranes tends to be much more difficult to achieve, and the margin for error in the number of pathways that can remain blocked and still maintain an acceptable permeability level is much smaller than it is for high air permeability fabrics.
What is needed in the art is an effective method and apparatus for cleaning semipermeable fabrics used in papermaking machines. Specifically, the method and apparatus needs to be vigorous enough to remove a high percentage of debris from a set of openings from which the removal thereof tends to be difficult.
The present invention provides a method and apparatus for cleaning a semipermeable membrane in which a cleaning fluid is applied thereto and then flushed therethrough using an air press to thereby clean the semipermeable membrane.
The invention comprises, in one form thereof, an apparatus for cleaning a semipermeable membrane, the semipermeable membrane being configured for carrying a fiber web. The apparatus includes a source of a cleaning fluid and an applicator configured for applying the cleaning fluid to the semipermeable membrane. The apparatus also includes an air press configured for carrying the semipermeable membrane therethrough. The air press having pressurized air therein is thereby configured for flushing the cleaning fluid through the semipermeable membrane.
The invention comprises, in another form thereof, a method of cleaning a semipermeable membrane, the semipermeable membrane being configured for carrying a fiber web. The method includes the steps of providing a cleaning fluid and applying the cleaning fluid on the semipermeable membrane. Further, an air press configured for carrying the semipermeable membrane therethrough is provided, and the air press has pressurized air therein. The semipermeable membrane is conveyed through the air press and is subjected to the pressurized air within the air press. The pressurized air thereby flushes the cleaning fluid through the semipermeable membrane.
An advantage of the present invention is that it provides an effective way of cleaning a semipermeable membrane having a low air permeability.
Another advantage is that it provides an effective way of cleaning a semipermeable membrane without disturbing paper quality.
Yet another advantage is that the cleaning press of the present invention can be combined with an air press used for dewatering and/or can be used for impregnating/coating the paper web.